The present invention relates in general to memory storage devices for use in a random access memory (RAM), and more particularly to memory cells of the so-called static type.
A typical static memory cell utilizes various devices such as transistors, diodes or resistors to provide three basic functions, namely switching transistors whose state of actuation indicates the bit of data stored in the cell, load impedance devices to supply power to the switching transistors, and coupling devices to provide access to a cell during a read or write operation. Conventionally, each memory cell is comprised of three pairs of devices, with one pair being assigned to each of the three basic functions, respectively.
As the capacity of integrated circuit memory devices increases, it is desirable to reduce the size of individual memory cells so that they require less silicon "real estate." Toward this end, memory cells have been developed that require fewer devices by combining at least two of the basic functions in a single device. For example, one type of memory cell that employs only four devices is known as the translinear cell. In this type of cell, the load and coupling functions share a single pair of bipolar transistors. More particularly, bit lines that transmit data to and from a cell also provide power to the cell through these shared transistors. Examples of such translinear memory cells are disclosed in U.S. Pat. Nos. 4,032,902 and 4,112,511.
Translinear memory cells have been effective in reducing the total size of a memory chip having a given storage capacity, and it is desirable to improve upon certain aspects of these cells. For example, one restriction that is associated with some of these types of cells is the limited read signal that can be obtained. In particular, if attempts are made to increase the read signal from a cell beyond a relatively low amplitude, the data stored in other cells might be disturbed. As a result, reading circuitry having a fairly high level of sensitivity must be employed to accurately detect the information stored in the cells.
Accordingly, it is a general object of the present invention to provide a novel static memory cell having reduced space requirements.
It is a more specific object of the invention to provide a novel translinear static memory cell that is capable of providing an easily detectable read signal while maintaining the integrity of the stored data.
It is a further object of the present invention to provide such a memory cell that enables information to be written into a cell during a relatively short period of time to thereby increase the operating speed of such cells.